The invention relates to a hydraulic underreamer and improved sections for use therein.
A hydraulic underreamer is used to hydraulically wash out or more typically enlarge a wellbore extending through a subterranean formation to thereby create a cavity in the formation. Hydraulic underreaming can be applied to a coal formation ("coal seam") to enhance the production of methane flowing from fractures ("cleats") in such a formation, or to other formations in which enlargement of a wellbore is desired.
One type of hydraulic underreamer includes: a packer section for sealing against a well casing so as to isolate an annulus above the packer section as defined between the casing and a work pipe; a cutting section for hydraulically enlarging a wellbore below the casing to thereby produce a mixture of liquid and formation fragments in the resulting cavity; and a jet pump section for pumping mixture from the cavity for passage through the above-mentioned annulus to the surface.